Incorporation of particles as fillers in rubber compositions are well known. The fillers are chosen to enhance certain characteristics of the rubber composition. For example, fillers may be used to enhance stiffness, hardness, modulus and so on.
U.S. Pat. Nos. 5,395,891 and 6,127,488 to Obrecht disclose the use of crosslinked polybutadiene and crosslinked styrene-butadiene copolymers respectively as a type of filler. The benefits of the inclusion of these crosslinked polymer particles is lower hysteresis while the polybutadiene gels also impart improved abrasion resistance and the styrene-butadiene copolymer gels offer improve wet traction.
U.S. Pat. Nos. 6,133,364, 6,207,757, and 6,242,534 to Obrecht et al. discloses a rubber composition comprising a crosslinked elastomer particle and a non-crosslinked elastomer. The crosslinked elastomeric particles are functionalized to impart unique surface reactivity for improved coupling with the non-crosslinked host elastomer as well as the subsequent ability to employ coupling agents other than the conventional sulfur-bridged bis-alkoxy silanes. The benefits of the gels are reported to be lower hysteresis, improved abrasion resistance, and improved wet traction.
U.S. Patent Applications published as US 2002/0007011 and US 2001/0053813 to Konno et al. disclose a rubber composition comprising as essential components a crosslinked polymer particle and a non-cross inked rubber component. The rubber composition may be used to obtain a vulcanized rubber. The crosslinked polymer particles are intended for use as a filler to provide a rubber composition having good processability and handling performance as well as improved tensile strength and wearing resistance when vulcanized. However, it has been found that the particles disclosed in the Kono et al. application tend to soften at higher service temperatures. The effectiveness of the particles as reinforcing fillers is therefore decreased.
When polymers are compounded, the interaction between molecules plays a significant role in dispersibility, processability, and other characteristics. Additionally, it has been demonstrated that when polymers of sufficiently different solubility parameters are compounded together the degree of immiscibility leads to an increase in the tangent delta at the Tg of the component rubbers. In this way, it is possible to improve the wet traction of a polymer composite as indicated by tangent delta at a temperature of xe2x88x9210xc2x0 C.
In the present invention, functional groups may be located on both the crosslinked particles and the host polymer. The purpose of functionalization in both the host polymer and the crosslinked particle is to improve the dispersion of the crosslinked particles while creating an interaction between the two materials so as to provide additional reinforcement.
The present invention capitalizes on the use of crosslinked polymer particles as reinforcing fillers that retain desirable physical properties at service temperatures of up to at least 150xc2x0 C. The present invention further exploits the interaction between the functionality of the filler particles and the host polymer. Performance characteristics such as lower hysteresis, improved tread wear and improved wet traction are exhibited by the rubber composition of the present invention. Further, functionality at the surface of the crosslinked particles may be varied so as to tailor specific interactions with alternative coupling agents to achieve desired performance characteristics.
As noted above, benefits of the inclusion of crosslinked polymer particles is lower hysteresis, improved abrasion resistance and/or improved wet traction. In order to maximize the benefit of the gels, it is reasonable to assume that they must be either chemically or physically connected to the host elastomer. For this reason, the application of polyisoprene gels, for which isoprene cures more readily than butadiene, is an advantage in most host polymers.
Also, the polymeric crosslinked particles are by nature deformable and do not yield the high modulus that rigid fillers do. Therefore, crosslinked particles that are resinous would have the advantage of yielding higher modulus.
The present invention is directed to a rubber composition comprised of a crosslinked polymer particle and a noncrosslinked host polymer. The inventive rubber composition comprises about 10 to about 70 parts by weight of the crosslinked polymer particle and about 30 to about 90 parts by weight of the noncrosslinked host polymer.
More particularly, in accordance with the invention, the crosslinked polymer particle is comprised of repeat units which are comprised of (a) about 0% to about 25% by weight of a conjugated diene unit, (b) at least 70% to about 85% by weight of an aromatic vinyl unit, (c) about 15% to about 30% by weight of a crosslinking monomer unit, and (d) about 0.1% to about 30% by weight of a functionalized monomer unit having one polymerizable unsaturated group and at least one functional group wherein said functional group provides for improved interaction with the host polymer or selected coupling agent or augments the vulcanization of the material. The preferred functional groups arc selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, and a siloxane.
The crosslinked polymer particle is carried in a non-crosslinked host polymer wherein the non-crosslinked host polymer is at least one member selected from the group consisting of a polymer having only conjugated diene repeat units, a polymer having repeat units of a conjugated diene unit and an aromatic vinyl unit, a polymer having repeat units of a conjugated diene unit and an xcex1-xcex2-unsaturated nitrile unit, an acrylic rubber, a polymer having repeat units of an ethylene unit, and polymers having repeat units having functional groups able to interact with the at least one functional group of the crosslinked polymer particle.
If present in the crosslinked polymer particle, the conjugated diene unit is at least one member of the group consisting of 1,3-butadiene, 2,3-dimethyl-1,3-butadiene and isoprene.
In the crosslinked polymer particle, the aromatic vinyl unit is at least one member of the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, xcex1-methyl styrene, 2,4-dimethylstyrcne, 2,4diisopropylstyrene, 4-tert-butylstyrenc and tert-butoxystyrene.
In the crosslinked polymer particle, the crosslinking monomer unit is at least one member of the group consisting of divinyl benzene, diisopropenylbenzene, divinylether, triallyl cyanurate, triallyl isocyanurate, 1,2-polybutadiene, ethyleneglycol dimethacrylate, propyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane dimethacrylate, trimethylolpropane trimethacrylate.
In the crosslinked polymer particle, the functionalized monomer unit comprises at least one member of the group consisting of an amino group, a hydroxyl group, an epoxy group, a carboxylic group and a siloxane group.
The invention discloses a rubber composition comprising a crosslinked polymer particle wherein the particle size is not greater than about 1000 nm.
The invention further discloses a rubber composition comprising a crosslinked polymer particle wherein the crosslinked polymer particle has a predetermined Tg such that the crosslinked polymer particle does not soften at service temperatures up to about 150xc2x0 C.
In accordance with the invention, there is provided a crosslinked polymer particle comprising repeat units which are comprised of (a) about 0% to about 25% by weight of a conjugated diene unit; (b) at least 70% to about 85% by weight of an aromatic vinyl unit; (c) about 15% to about 30% by weight of a crosslinking monomer; and, (d) about 0.1 to about 30% by weight of a functionalized monomer unit having one polymerizable unsaturated group and at least one functional group.
The invention further discloses a rubber composition comprising (1) from about 10 to about 70 parts by weight of a crosslinked polymer particle which is comprised of as repeat units which are comprised of: (a) up to about 25% by weight of a conjugated diene unit, (b) at least 70% by weight of an aromatic vinyl unit, (c) at least 15% by weight of a crosslinking monomer, and (d) about 0.1 to about 30% by weight of a functionalized monomer unit having one polymerizable unsaturated group and at least one functional group; and, (2) from about 30 to about 90 parts by weight of a non-crosslinked host polymer wherein the noncrosslinked host polymer is at least one member selected from the group consisting of a polymer having only conjugated diene repeating units, a polymer having repeating units of a conjugated diene unit and an aromatic vinyl unit, a polymer having repeating units of a conjugated diene unit and an xcex1-xcex2-unsaturated nitrile unit, an acrylic rubber, a polymer having repeat units of an ethylene unit, and polymers having repeating units having functional groups able to interact with a functional group of the functionalized monomer.
The invention further discloses a rubber composition comprising 1) from about 10 to about 70 parts by weight of a crosslinked polymer particle comprising polyisoprene; and, 2) from about 30 to about 90 parts by weight of a non-crosslinked host polymer wherein the non-crosslinked host polymer is at least one member selected from the group consisting of a polymer having only conjugated diene repeat units, a polymer having repeat units of a conjugated diene unit and an xcex1-xcex2-unsaturated nitrile unit, an acrylic rubber, and a polymer having repeat units of an ethylene unit.
In the description of the invention, any reference to xe2x80x9cTgxe2x80x9d refers to a xe2x80x9cglass transition temperaturexe2x80x9d. A preferred method of measuring the Tg is by using a differential scanning calorimeter at a heating rate of 10xc2x0 C. per minute.
The term xe2x80x9cfunctionalizationxe2x80x9d refers to the presence of certain polar functional groups, preferably amino groups, hydroxyl groups, epoxy groups, or siloxane groups. The functional groups originate in functionalized monomers and are carried on the polymeric backbone of either the reinforcing filler as described herein, or on the host polymer, or both.
A xe2x80x9crepeat unitxe2x80x9d has its origins in a given monomer and is present in a polymeric molecule after polymerization.
The term xe2x80x9cinteractionxe2x80x9d as used herein refers to ionic-, covalent-, or hydrogen-bonding occurring in the processes of the present invention.
Reference to xe2x80x9chost polymerxe2x80x9d includes a polymeric matrix or polymer blend.
The present invention is directed to a rubber composition comprised of from about 10 to 70 parts by weight of a crosslinked polymer particle and from about 30 to about 90 parts by weight of a noncrosslinked host polymer. In the preferred embodiment, the rubber composition is comprised of about 10 to about 50 parts by weight of the crosslinked polymer particle. In a more preferred embodiment, the rubber composition is comprised of about 10 to about 30 parts by weight of the crosslinked polymer particle.
In the preferred embodiment, the crosslinked polymer particle is comprised of repeat units which are comprised of (a) about 0% to about 25% by weight of a conjugated diene unit, (b) at least 70% to about 85% by weight of an aromatic vinyl unit, (c) about 15% to about 30% by weight of a crosslinking monomer unit, and (d) about 0.1% to about 30% by weight of a functionalized monomer unit having one polymerizable unsaturated group and at least one functional group. In the preferred embodiment, the at least one functional group is selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, and a siloxane.
The crosslinked polymer particle is carried in a non-crosslinked host polymer wherein the non-crosslinked host polymer is at least one member selected from the group consisting of a polymer having only conjugated diene repeat units, a polymer having repeat units of a conjugated diene unit and an aromatic vinyl unit, a polymer having repeat units of a conjugated diene unit and an xcex1-xcex2-unsaturated nitrile unit, an acrylic rubber, a polymer having repeat units of an ethylene unit, and polymers having repeat units having functional groups able to interact with at least one functional group of the crosslinked polymer particle.
In accordance with the invention, in the preferred embodiment, in the crosslinked polymer particle, the conjugated diene unit may be formed from at least one member of the group consisting of 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and isoprene; the aromatic vinyl unit may be formed from at least one member of the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, xcex1-methyl styrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, and tert-butoxystyrene; the crosslinking monomer unit may be formed from at least one member of the group consisting of divinyl benzene, diisopropenylbenzene, divinylether, triallyl cyanurate, triallyl isocyanurate, 1,2-polybutadiene, ethyleneglycol dimethacrylate, propyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane dimethacrylate, trimethylolpropane trimethacrylate; and the functionalized monomer unit may comprise at least one member of the group consisting of an amino group, a hydroxyl group, an epoxy group, a carboxylic group and a siloxane group.
In the present invention, the crosslinked polymer particle could potentially be produced separately as a reinforcing filler or as a masterbatch with emulsion rubber that would lower the density of the compound, maintain rolling resistance, improve wear, and improve wet traction.
Further, in accordance with the present invention, resinous crosslinked polymer particles exhibiting high Tg may provide serviceability of the invention up to about 150xc2x0 C.
Polar functionalization of higher Tg emulsion gel particles (elastomer or resin) offers the ability to decrease the compatibility between the host polymer or blend and the reinforcing particles, thereby increasing the tangent delta (tan xcex4) at low temperatures and increasing wet traction. Utilizing the chemistry occurring at the surface of the particles, new coupling agents could be employed to impart desired characteristics to a vulcanized rubber formed from the inventive rubber composition.
In the preferred embodiment, the crosslinked polymer particle has a particle size of 1000 nm or less, more preferably 500 nm or less and most preferably about 100 nm to about 240 nm. It is contemplated that a particle size as low as about 40 nm will still provide the advantages of the present invention.
This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.